1. Field of the Invention
The present invention relates to an image pickup system for performing an estimation for a spectral characteristic related to a subject or an illumination light, in particular, an image pickup system capable of preventing generation of an estimation error due to generation of a noise included in an image signal, a false color accompanied by an interpolation processing, a motion blur of the subject, or the like, and realizing a high accuracy estimation for a spectral characteristic.
2. Description of the Related Art
As a conventional technology for performing an estimation for an unknown spectral characteristic related to a subject or an illumination light, such a method has been proposed that a plurality of image signals having different spectral characteristics for each shooting operation are obtained by utilizing presence or absence of an external illumination, insertion of a filter into a light path, image pickup devices having different spectral characteristics, and the like, and the spectral characteristic is approximately calculated from these image signals. For example, Japanese Unexamined Patent Application Publication No. 2001-78202 discloses such an example that two types of image signals having different spectral characteristics for each shooting operation are obtained by utilizing presence or absence of a flash lamp light and insertion of a fitter into a light path, modeling of the spectral characteristic that should be estimated is performed through linear combination of a small number of basis functions, and a weighting coefficient with respect to the above-mentioned basis functions is calculated from the above-mentioned two type of image signals for performing the estimation. With this configuration, without depending on the illumination light for each shooting operation, it is possible to obtain the spectral characteristic of the reflected light of the subject (hereinafter, which is simply referred to as spectral characteristic of the subject), and the image signal can be generated under an arbitrary illumination condition. Also, Japanese Unexamined Patent Application Publication No. 2004-186879 discloses such an example that two types of image signals having different spectral characteristics for each shooting operation are obtained by using two types of pixels having different spectral characteristics, and a type of a light source of an illumination light for each shooting operation is estimated. With this configuration, even for the shooting operation under a plurality of light sources, it is possible to perform a satisfactory white balance processing. Furthermore, Japanese Unexamined Patent Application Publication No. 2005-311581 discloses such an example that by shooting in advance a color code chart or the like whose spectral characteristic is known, the spectral characteristic of the subject under an arbitrary illumination condition is estimated. With this configuration, various color processing can be realized.
According to the method of estimating the unknown spectral characteristic related to the subject or the illumination light on the basis of the plurality of image signals having different spectral characteristics for each shooting operation, an inverse matrix of a system matrix related to an image sensor system or a pseudo inverse matrix based on a singular value decomposition is utilized.